X-ray apparatus



Dec. 16, 1958 MORRISON 2,864,958

X-RAY APPARATUS Filed Aug. 13, 1957 Fla. 1.

INVENTOR. MON T F 0RD MORE/$0 United States PatentO The present invention relates generally to systems and methods for providing stabilization of voltages across a load in alternating current circuits, it relates more particularly to such systems and methods that employ electron discharge structures as a voltage stabilization means, and more specifically to such systems and methods that employ X-ray tubes in the load circuit.

Among the objects of this invention are: to provide a system and method which operates to stabilize the voltage across an X-ray tube by causing the X-ray tube voltage itself to control the stabilization; to provide an X-ray tube transformer load which balances the load on the X-ray tube transformer, making a symetrically loaded system with the resultant symmetrical wave forms of voltage and current in the system which permits of greater simplicity and much more dependable structures in the control circuits; to provide a novel feed-back circuit from the load voltage to the transformer control circuit, in which X-ray tube filament transformers are formed to operate in the second role of feed-back capacitors, thereby not only eliminating the capacitance load on the X-ray tube transformer which would be imposed thereon by separate feed-back capacitors, but also eliminating the necessity of separate feed-back capacitors altogether.

The present invention, although it is disclosed as an X-ray structure and method, obviously it may be embodied in any equivalent structure and in any equivalent method.

In the prior art of self-rectifying X-ray tube operating apparatus, the resultant wave forms of voltages and currents are so distorted by the unbalanced load due to the X-ray tube, that stabilization of the tube voltage by circuit control has never been accomplished to any noteworthy degree. The difi'iculties encountered in such art are set forth to some extent in the applicants Patent Number 2,495,122, issued January 17, 1950.

The specific nature of this invention, as related to X-ray tube operation, resides importantly in the art of self-rectifying X-ray tube operation where half-wave operationon the X-ray tube transformer unbalances all the connected circuits and the present invention not only balances the connected circuits, but definitely stabilizes them in this balanced condition by primary control from the X-ray tube voltage itself.

In the art of noncontacting thickness gauges, where X-ray radiation is employed as a means of determining the thickness of a material under measurement, the problem of stabilization of the X-ray tube voltage to a high degree of constancy is an all-important factor in the accurate determination of the thickness measured.

In the above-mentioned art, the conventional circuit employed is that of one self-rectifying X-ray tube imposed as a load on the secondary of a step-up alternating current transformer. I

In the referred-to gauge art, two X-ray tubes may be employed to an advantage since two focal spot sources of X-rays are not a disadvantage and the double energy is an advantage because of the double signal energy to filament transformer shown in'area B are equivalents of p those described. Referring to Fig. 1, 21 is a primary the noise energy ratio attained in the amplifiers employed in the measurement of the X-ray energy used todetermine the thickness measured in such gauges.

The various features and advantages of this. invention-L. will appear from the detailed description and claimswhenw taken with the drawings in which: t

Fig. 1 is a circuitillustrating oneembodiment of invention,

Fig. 2 is a circuit'illustrating a second embodiment of the invention, and p I .1- i Figs. 3 and 4 are end and side elevations, respectively, of a novel ancillary structure employed in the embodiments illustrated herein and which comprises an X-Ia'yZ tube filament-transformer having 'afeecl-back capacitorj structure formed in it.

In the circuit diagram of Figal, 1 is a source of alter-i i' nating voltage, 2'is a step-up X-ray tube transformer having center tapped primary 3, and a center tapped second-' ary 4, which may be grounded as illustrated, if and. when 1 desirable.

Further,-5 and 6 are grid:'or'otherwise electrode controlled electron discharge structures which may befincluded in the same envelope, if and when desirable, but

are illustrated as two separate triodes, however the number of'electrodes em'ployed' in-s'eparate envelopes or in v a single envelope is not a critical limitation, so'longias each structure has at least one control electrode, Which' is referred to hereunder as a grid. t

Structures 5 and 6, hereinafter referred'to as triodes 5 and 6, have respectively a plate 7, a grids, a cathode 9, and a plate 10, a grid;11,.and a cathode 12.

Alternating voltage source 1 is connected to the center# tap13 of transformer primary 3 and at point 14 toa" cathode bias resistor 15Yand'through this resistor to the grounded triode lead 16. The triodes are thuslyncon nected in the conventional push-pull manner including the primary of the transformer '2, but withan alternating'i voltage plate supply.

zT-ransformeri'isecondary'4 is connectedbyle ads 17 and 18 to X-ray tubes 19' and 20. X-ray -tubes 19 and 20': are connectedto-leads 17 and 18 in opposite conductivity-f relation so that the two X ray tubes jointly provide 'an uninterrupted resistive load'to the voltage of secondary- 4, or one might describe the load as one of full wave rectification with high resistance rectifiers. Itwillbe" obvious to those skilled vin the art' to which the invention appertains,'that the two X-ray tubes thus connected, have a loadequivalent in any nondirectional circuit resistance! It is further obvious that the invention is independent of b whether the X-ray radiation from both X-ray tubes is i used, or even from one alone.

Dotted areas A and B contain symbolic elements of an X-ray -tube filament transformer, to be described in greater detail hereinafter.

fled, it being understood that the similar details of the winding which may be connected, as conventionally indi has an electrostatic shield 24 connected to it which forms the other plate of the capacitor stated, which will be referred to as capacitor 23-24. The similar capacitor of the filament transformer shown in area .B, will be referred to as capacitor 2627. In Fig. 1, 28 is a st epdown transformer having a center tapped highvoltage,

primary winding 29,Whi0l1 obtains feed-back energy Patented Dec. 16, 1958 For "the purpose of fully understanding the operation of Fig. l, the details of the filament transformer, shown in the area A will be identiof the winding may be grounded as shown, if and when desirablev t The secondary 30 of transformer 28, is shunted by capacitor 31, and the terminals of secondary 30 are connected to grids 8 and 11, as shown, in the conventional manner.

The generalized functioning of the structure shown in Figil, can bestated in conventional terms, as will be given hereunder, but the detailed operation cannot be statedcorrcctly without employing the theory of such circuits which is only correctly set forth in the applicants Patent Number 2,587,750issued March 4, 1952.

Inconventional terms, it can be stated that the stabilization of the X-ray tube voltage in the circuit shown in Fig. l, is attained by feeding back the voltage across the X-ray tubes to the grids of the push-pull triodes through conventional circuit components having predetermined parameters and fixed circuit alignments, with which an increase in X-ray tube voltage causes an increase in negative potential applied to the grids of the push-pull triodes, also in a reversed algebraic sense when the voltage decreases. Since the triodes may have a considerable amplification factor, small variations in X ray tube voltages produce amplified effects in transformer 2.. With the proper-circuit parameters and proper circuit alignments, a stabilization point may be reached where the degree of constancy of the X-ray tube voltage is largely inversely proportional to the amplification factor of the system.

Since. the applicant has found that the phase angles, between the gridvoltages and the plate voltages in such a circuit asdisclosed, are not. described correctly and stated correctly in the literature other than in his abovereferred-to patent, reference is made thereto for an understandingof the terms used in the specification and claims hereof, that are not found elsewhere.

Indetermining. the parameters and the alignments of the feed-back circuit comprising capacitor 2324, capacitor 26-27, high-voltage primary winding 29, low-voltage secondary winding 30 and its shunted capacitor 31, the proper grid operating voltage angle (see Patent 2,587,750 for definition and theory thereof) can be determined as fully taught in that patent. With the grid operating voltage angle (g. o. v. a.) determined, the several circuit components identified by the numerals 2324, 26-27, 29, 30 and. 31, can have their values determined by wellknown conventional methods, to cause the proper g. o. v. a. of the correct voltage amplitude for operation under stabilization of the X-ray tube voltage.

It is believed that a repetition in this application of the theory set forth in the patent referred to above, would be redundant.

Referring to Fig. 2, this1diagrammatic drawing, with the exception of the grid circuit, is identical with Fig. l, and therefore the elements of Fig. 2 that are identical with the corresponding elements of Fig. 1, will not have a repeated description here, and only the changed grid circuit will be described and discussed.

Assuming familiarity with Fig. 1, Fig. 2 will be referred to and in which transformer secondary winding 30, is provided with a system of full-wave rectification employing rectifiers 32 and 33, having a load resistor 34, shunted by capacitor 35. The voltage developed across resistor 34 and capacitor 35, provides a negative biasfor the push-pull grids. The amount of current from source 1 passed through the push-pull triodes and primary 3, is

inversely proportional to the negative grid bias voltage, in an amplified ratio.

When the voltage across the X-ray tubes 19 and 20, rises, the gridbias voltage rises, lowering the current flow through the. transformer primary -3, also in a reversed algebraic sense when the voltage across the X-ray tubes 4 falls. This effect is, as stated above, largely inversely proportional to the amplification factor of the system.

Fig. 2 thus operates as does Fig. 1, so far as result is: concerned, but has the advantage that the g. o. v. a. doesnot have to be reckoned with in the structure, as the grid control voltage in this case is substantially continuous and not sinusoidal as in the case of Fig. 1.

Referring to Figs. 1, 3 and 4, 22 is a cruciform scctioned laminated steel transformer core of the conventional so-called core type, 21 is the primary winding,. 36 is an insulating bushing surrounding the primary winding, 23 is a longitudinally split metallic sleeve forming one plate of the feed-back capacitor which is com-- pleted by a second plate comprising a longitudinally split sleeve 24, mounted upon an insulating bushing 37. The sleeve 23 extends to the entire length of the core window. The secondary winding 25 of the transformer is wound on the plate 24, to which it is electrically connected, as shown in Figs. 1 and 2.

The above-described transformer is obviously the filament transformer of Figs. 1 and 2, which not only serves as a filament transformer but also as a feed-back capacitor between the X-ray tube voltage and the grid control circuits of the push-pull triodes. This combination structure of filament transformer and feed-back capacitor, not only effects a large saving over the employment of separate high-voltage (up to 300,000 volts) capacitors, but further reduces the capacity load on the X-ray tube transformer, which load would be present with separate feed-back capacitors, and since there is considerable inherent secondary to primary electrostatic capacity in X-ray tube filament transformers, this capacity has to be increased only slightly by some small amounts of added surface to the effective electrostatic contours of the primary and secondary windings.

It is obvious from inspection of Figs. 1 and 2, that the load circuits of transformer 2 are perfectly balanced with reference to the alternating current flow therein.

I claim:

1. In an Xray apparatus including a source of alternating voltage connected to the primary of a step-up transformer having its secondary supplying electrical energy to two X-ray tubes connected in a parallel relation providing both directions of circuit-conductivity load on the transformer,-a step-up transformer having a primary and a secondary, a source of alternating voltage, two electron discharge structures each having a control grid and said structures connected between said source and said primary limiting the flow of current from source to primary under control of said grid when energized, a balanced voltage load on said secondary including two X-ray tubes connected in a parallel relation providing both directions of electrical circuit conductivity, and a feedback circuit receiving energy from a parallel connection with said two X-ray tubes and applying a portion of it to said control grids, whereby the current fiow from said source to said transformer is under feed-back circuit control by the voltage appliedto the two X-ray tubes.

2. In an X-ray apparatus including a source of alternating voltage connected to the primary of a step-up transformer having its secondary supplying electrical energy to two X-ray tubes connected in a parallel relation providing both directions of circuit-conductivity load on the transformer, a step-up transformer having a primary and a secondary, a source of alternating voltage, two electron discharge structures each having a control grid and said structures connected between said source and said primary limiting the flow of current from source to primary under control of said grid when energized, a balanced voltage load on said secondary including two X-ray tubes connected in a parallel relation providing both directions of electrical circuit conductivity, a feed-back circuit receiving energy from a parallel connection with said two X-ray tubes and applying a portion of it to said control grids, said feed-back circuit including a step-down transformer with a capacitance loaded secondary connected to said control grids, and said capacitance loading in cooperation with coupled circuit inductance causing the correct grid operating voltage angle for said electron discharge structures under predetermined operation thereof, whereby the current flow from source to said transformer is under feed-back circuit control by the voltage applied to the two X-ray tubes.

3. In an apparatus including a source of alternating voltage connected to the primary of a step-up transformer having its secondary supplying electrical energy to two X-ray tubes connected in-a parallel relation providing both directions of circuit-conductivity load on the transformer, a step-up transformer having a primary and a secondary, a source of alternating voltage, two electron discharge structures each having a control grid and said structures connected between said source and said primary limiting the flow of current from source to primary under control of said grid when energized, abalanced voltage load on said secondary including two X-ray tubes connected in a parallel relation providing both directions of electrical circuit conductivity, a feed-back circuit receiving energy from a parallel connection with said X-ray tubes and applying a portion of it to said control grids, and said feed-back circuit including a stepdown transformer having a full-wave rectifier in the secondary thereof, the output of which is connected to the control grids of said electron discharge structures, whereby the current flow from source to said transformer is under feed-back circuit control by the voltage applied to the two X-ray tubes.

4. In an X-ray apparatus including a source of alternating voltage connected to the primary of a step-up transformer having its secondary supplying electrical energy to two X-ray tubes connected in a parallel relation providing both directions of circuit-conductivity load on the transformer, a step-up transformer having a primary and a secondary, a source of alternating voltage, two electron discharge structures each having a control grid and said structures connected between said source and said primary limiting the flow of current from source to primary under control of said grid when energized, a balanced voltage load on said secondary including two X-ray tubes connected in a parallel relation providing both directions of electrical circuit conductivity, a highvoltage-insulated filament transformer for each of said two X-ray tubes, a feed-back circuit receiving energy from a, parallel connection with said two X-ray tubes and applying a portion of it to said control grids, and said feed-back circuit transmitting energy by means of the primary to secondary electrostatic capacity of said filament transformers, whereby the current flow from said source to said transformer is under feed-back circuit control by the voltage applied to the two X-ray tubes.

5. In an X-ray apparatus including a source of alternating voltage connected to the primary of a step-up transformer having its secondary supplying electrical energy to two X-ray tubes connected in a parallel relation providing both directions of circuit-conductivity load on the transformer, a step-up transformer having a primary and a secondary, a source of alternating voltage, two electron discharge structures each having a control grid and said structures connected between said source and said primary limiting the flow of current from source to primary under control of said grid when energized, a balanced voltage load on said secondary including two X-ray tubes connected in a parallel relation providing both directions of electrical circuit conductivity, a highvoltage-insulated filament transformer for each of said two X-ray tubes, a feed-back circuit receiving energy from a parallel connection with said two X-ray tubes and applying a portion of it to said control grids, said feed-back circuit transmitting energy by. means of the primary to secondary electrostatic capacity of said filament transformers and including a stepdown transformer with a capacitance loaded secondary tion thereof, whereby the current flow from said source to said transformer is under feed-back circuit control by the voltage applied to the two X-ray tubes.

6. In an X-ray apparatus including a source of alternating voltage connected to the primary of a step-up transformer having its secondary supplying electrical energy to two X-ray tubes connected in a parallel relation providing both directions of circuit-conductivity load on the transformer, a step-up transformer having a primary and a secondary, a source of alternating voltage, two electron discharge structures each having a control grid and said structures connected between said source and said primary limiting the flow of current from source to primary under control of said grid when energized, a balanced voltage load on said secondary including two X-ray tubes connected in a parallel relation providing both directions of electrical circuit conductivity, a highvoltage-insulated filament transformer for each of said two X-ray tubes, a feed-back circuit receiving energy from a parallel connection with said two X-ray tubes and applying a portion of it to said control grids, and said feed-back circuit transmitting energy by means of the primary to secondary electrostatic capacity of said filament transformers and including a step-down transformer having a full-wave rectifier in the secondary thereof, the output of which is connected to the control grids of said electron discharge structures, whereby the current flow from said source to said transformer is under feedback circuit control by the voltage applied to the two X-ray tubes.

References Cited in the file of this patent UNITED STATES PATENTS 2,523,247 Glick Sept- 19, 1950 2,554,041 Lundahl May 22, 1951 2,617,045 Coe Nov. 4, 1952 2,626,360 Wright Jan. 20, 1953 

